The present invention relates generally to anti armor weaponry, and more particularly to detached and attached thermal spoilers for fins of kinetic energy projectiles.
Typically, kinetic energy projectiles are launched from gun tubes of tanks or other weaponry tubes against enemy tanks or other hard targets to cause total, or at least, partial destruction and thereby disable the target. Damage to the target is caused by the kinetic energy (1/2.times.mass .times.velocity.sup.2) of the projectile, because the projectile contains no explosive charge. Such projectiles are fin-stabilized and therefore, are designed not to undergo significant spin in flight, but rather to maintain a trajectory path with high velocity (usually Mach 5 or higher, equal to 5500 feet per second, or greater) for short flight durations (e.g., from one to three seconds). By the time impact occurs, the projectile fins have been heated to sufficiently high temperature as a result of its velocity, shape and travel distance. The force of the impact causes the projectile and the target structure at the point of impact to disintegrate into fragments capable of igniting the impacted tank's fuel and shells. A direct hit will usually cause an explosion or sufficient damage to be disabling, even if the target is not completely destroyed.
During firing range tests of kinetic energy projectiles it has been found that the fins of the projectile suffer loss of major portions of their surfaces. Such losses are attributable, principally, to in-flight metal burning, and secondarily, to inbore contact with the propellant granules during the projectile release from its propellant charge case. The projectile is typically composed of tungsten or high density material, while the fins are usually of aluminum. Fins retrieved from the fired projectiles show a loss in excess of fifty percent of their original surface area and a substantially degraded fin edge and shape. In particular, the leading edges of the fins of the spent projectile have severe loss of smooth line of the leading edge to become rough-edged, and the shape of the edges usually differ considerably from fin to fin. The surfaces remaining of the different fins mounted on the same projectile also reveal asymmetrical shapes.
It may be tolerated that there be some burning of the fins during flight because less fin material on the projectile increases its penetration on impact. However, if the fin loss is too great or in the wrong place it can cause instability of the projectile during flight. FIGS. 1 and 2 are side and end views, respectively, of a typical prior art kinetic energy projectile 10 in which the body 11 has a large overall length to diameter ratio and the forebody 12 is almost pointed. The projectile has surface groovings 13 and at least one set of multiple fins 14. At typical speeds reached in flight and with such a configuration, the fin axial air resistance force (which is a measure of the drag force) is the major contributor to the total projectile axial resistance force. Accordingly, current design techniques seek to avoid increasing such fin axial resistance force.
It is a principal object of the present invention to passively reduce the fin metal burning during flight of the projectile.
Firing range test results on launched projectiles also demonstrate that the projectile suffers from some yawing (lateral) motion, which causes oblique impact with the target. Although the yawing motion may be small, it tends to prevent complete penetration of the target by the projectile, and is at least partly attributable to lack of symmetrical burning of the multiple fins.
It is a more specific object of the present invention to reduce the fin burning through the use of a shielding (or spoiler) fin, and basic aerodynamic and heat transfer features that aid in reducing fin temperature in flight.